Field-induced slow magnetic relaxation from linear trinuclear CoIII-CoII-CoIII to grid [2 x 2] tetranuclear mixed-valence cobalt complexes

By employing the ligand azotetrazolyl-2,7-dihydroxynaphthalene (H(3)ATD), two linear trinuclear mixed-valence cobalt complexes [(CoCo2III)-Co-II(HATD)(4)(H2O)(4)]center dot 4DMA center dot 3H(2)O (1, DMA = N,N-dimethylacetamide) and [(CoCo2III)-Co-II(HATD)(4)(DMF)(2)(H2O)(2)]center dot 2DMF center dot 2H(2)O (2, DMF = N,N-dimethylformamide) were synthesized. Two [2 x 2] grid-like tetranuclear ion-pair complexes [(Co2Co2III)-Co-II(HATD)(4)(bpp)(2)(H2O)(2)][Co-III(HATD)(2)](2)center dot 8DMF center dot 6H(2)O (3, bpp = 2,6-di(pyrazol-1-yl)pyridine) and [(Co2Co2III)-Co-II(HATD)(4)(bpp)(2)(H2O)(2)][Co-III(HATD)(2)](2)center dot 8DMSO center dot 4MeOH (4, DMSO = dimethyl sulphoxide) were obtained by the reaction of complex 1/2 with tridentate-chelating bpp in DMF and DMSO, respectively. The single-crystal X-ray diffraction analysis indicated that complexes 1 and 2 have a similar core, in which the DMA in 1 acts as a guest molecule, and the DMF in 2 acts as a coordinated molecule and guest molecule. Complexes 3 and 4 are isostructural. All the Co(ii) ions in 1-4 are present in a distorted octahedral geometry. The ac susceptibility measurements show that all complexes display frequency-dependent peaks in the out-of-phase (chi(m)) component of the alternating-current (ac) magnetic susceptibility data, which is the characteristic behavior of single molecule magnets (SMMs).